Many power tools are provided with a three element plug because of the necessity of grounding the tool for safety reasons. Often, when using such tools, only a two element wall outlet socket is available, and also the outlet may be so remote that an extension cord is required. One solution to such a problem is to use a grounding adapter plug at the wall outlet and a three wire extension cord. However, such adapter plugs are frequently used in an unsafe manner by connection of the ground wire therefrom to the mounting screw of the cover plate of the wall outlet which may not be grounded. Also, three wire extension cords are rather expensive.